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They are alleged to include messages from several Arab countries urging the US to halt Iran's nuclear programme by military force if necessary, as well as instructions from Ms Clinton to US diplomats to spy on other countries at the United Nations.

The classified documents are said to also have highlighted Israel trying to prod a sometimes sceptical Washington into tougher action with sanctions, subversion and urging a military strike by 2011 against Tehran.

The Guardian newspaper, which helped to edit the material, said the release of the 250,000 cables could catapult the US into a global diplomatic crisis.

The White House has directed government agencies to tighten procedures for handling classified information after the leak.

The new procedures would ensure ‘that users do not have broader access than is necessary to do their jobs effectively, as well as implementation of restrictions on usage of, and removal media capabilities from, classified government directives,’ according to a directive from the Office of Management and Budget.